Electrorefined nickel of controlled size

ABSTRACT

An improved process for producing electrorefined nickel cathode material of controlled dimension and substantial thickness wherein the nickel is deposited upon a substantially flat, permanent metal cathode mandrel such as stainless steel, and having conductive islands of controlled size defined on the surface thereof, e.g., by the use of interconnecting lines of nonconductive resist, from a nickel electrorefining catholyte containing controlled amounts of sulfur dioxide and a leveling agent to facilitate adherence of the electrodeposited nickel upon the mandrel surface by controlling the stress level therein to a tensile value not exceeding about 6,000 pounds per square inch and thereafter stripping the nickel deposit from the mandrel to recover electrodeposited nickel in sizes corresponding to the original areas of the conductive islands and to recover the mandrel in a condition suitable for further plating.

United States Patent [191 Knapp ELECTROREFINED NICKEL OF CONTROLLED SIZE V [75] Inventor: Burton Bower Knapp, Allendale,

[73] Assignee: The International Nickel Company,

' Inc., New York, N.Y.

[22] Filed: March 11, 1971 [21] Appl. No.: 123,436

Related US. Application Data [60] Division of Ser. No. 683,801, Nov. 17, 1967, Pat. No. 3,577,330, which is a continuation-in-part of Ser. No. 338,309, Jan. 17, 1964, abandoned.

[52] US. Cl. ..204/12, 204/112, 204/281 [51] Int. Cl ..C23b 7/02, C22d 1/14, BOlk H00 [58] Field of Search ..204/12, 10, 281, 292, 112

[56] References Cited UNlTED STATES PATENTS 2,773,816 12/1956 Wesley et a1. ..204/12 2,706,170 4/1955 Marchese ..204/3 2,392,708 l/1946 Tschop ..204/292 FORElGN PATENTS OR APPLICATIONS 1,021,71 l 3/1966 Great Britain .h, ..204/12 1 Feb. 6, 1973 1,056,087 1/1967 Great Britain".. ..204/12 Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello Att0rney-Maurice L. Pine] [5 7] ABSTRACT An improved process for producing electrorefined nickel cathode material of controlled dimension and substantial thickness wherein the nickel is deposited upon a substantially flat, permanent metal cathode mandrel such as stainless steel, and having conductive islands of controlled size defined on the surface thereof, e.g., by the use of interconnecting lines of nonconductive resist, from a nickel electrorefining catholyte containing controlled amounts of sulfur dioxide and a leveling agent to facilitate adherence of the electrodeposited nickel upon the mandrel surface by controlling the stress level therein to a tensile value not exceeding about 6,000 pounds per square inch and thereafter stripping the nickel deposit from the mandrel to recover electrodeposited nickel in sizes corresponding to the original areas of the conductive islands and to recover the mandrel in a condition suitable for further plating.

1 Claim, No Drawings ELECTROREFINED NICKEL OF CONTROLLED SIZE 4 The present applicatiori isa division of UTS. Pat. No. 3,577,330, granted May 4, 1971 which is, in turn, a continuation-in-part application of U.S. application Ser. No. 338,309, filedJan. 17, 1964, now abandoned.

The present invention relates to the production of electrolytic nickel and, more particularly, to a process for producing electrolytic nickel in subdivided form. It is well known that the standard commercial high purity nickel (99.9+% nickel) is usually provided in the form of cathode sheets from an electrorefining operation. These sheets are usually about 28 inches by 38 inches in major dimension and are about three-eighths inch thick. in many industrial operations, these cathode sheets can be employed directly. However, in many other industrial operations, nickel must be provided in smaller sizes because the standard size cannot conveniently be used. The standard cathode sheets can be sheared to provide the smaller sizes required in operations such as induction furnace melting of nickel-containing alloys, nickel stock for electroplating using titanium baskets to hold the nickel stock, etc. However, it is desirable to provide electrolytic nickel in smaller sizes directly from the electrorefining operation while at the same time maintaining or improving the efficiency of the nickel electrorefining operation, and, thus, to eliminate the cost factors involved in shearing the standard cathode nickel sheets. The production of electrolytic nickel is well known and is described, for example, in the Renzoni U.S. Pat. No. 2,394,874.

It has now been discovered that throughthe use of a permanent cathode mandrel of special design, electrolytic nickel pieces of any desired size can be produced directly in the electrorefining operation while maintaining the 'efficiency of the operation at a high level.

It is an object of the present invention to p rovide a process for producing electrolytic nickel of controlled small size.

Another object of the invention is to provide a spe cial permanent mandrel for use as cathode in a nickel electrorefining cell.

The invention also contemplates providing ap'meess for producing electrolytic nickel having a low level of internal stress.

Othero bjects and aavama'ges'orme inventTon wilT become apparent from the following description.

Generally speaking, the present invention contemplates a process for producing electrolytic nickel in subdivided form which comprises immersing in an electrorefining bath a permanent, i.e., reusable, metal cathode mandrel having conductive islands defined on the surface thereof, electrodepositing nickel upon said cathode under conditions of low stress to provide electrolytic nickel deposits having substantial thickness upon said conductive islands, removing the plated cathode mandrel from said bath and removing the deposited nickel from said mandrel, so as to recover the mandrel for reuse.

The conductive islands are defined on the surface of the permanent metal cathode mandrel by means of interconnecting areas of nonconductive material. The mandrel may be provided in a number of ways. Thus, interconnecting lines of nonconductive or resist material at least as wide as the thickness of metal to be deposited upon the mandrel (i.e., generally about oneeighth to one-fourth inch) may be applied to the surface thereof to define isolated conductive areas, or islands, of the desired size and shape. The nonconductive resist material may be in the form of an adherent paint, varnish, lacquer, tape, etc., which will be retained on the mandrel surface and will be compatible with the electrorefining bath. Materials having a plastic or rubber base, e.g., epoxy resins, acrylics, polyethylenes, etc., are examples of such resists. The conductive cathode metal mandrel may be, for example, pure nickel or a nickel-chromium or nickelchromium-iron/alloy containing about 8 percent to 30 percent chromium, at least 8 percent nickel and up to about 74 percent iron, such as the well-known l8-8 stainless steel. Electroformed nickel is also satisfactory as the mandrel metal. In order that the mandrel will be sufficiently rugged to withstand repeated reuse, it is usually about 0.020 inch or about 0.040 inch up to about one-sixteenth or about one-eighth inch thick. The mandrel may be sufficiently thin, e.g., up to about one thirty-second inch thick, to be readily flexed for stripping the nickel deposit therefrom or may be considerably thicker and stiffer, e.g., about one-eighth inch thick. A pattern of interconnecting lines which are depressedwith respect to a major face of the mandrel may be embossed in the thinner mandrel sheets and the embossed lines may be filled or coated with resist. In such an instance, the mandrel may be made of two embossed sheets placed back-to-back so that plating may be conducted simultaneously upon both sides of the mandrel. Such embossed lines also perform the function of stiffening the thinner mandrel. It is advantageous to electroform mandrels containing such depressed interconnecting lines in a metal such as nickel. It is an advantage from the operating standpoint to employ the thicker and heavier mandrel sheets in electrorefining practice since good contact to the cathode bus bar is thereby achieved and the problem of warping and shorting in the plating tank is avoided. In order to promote adherence of the electrodeposited nickel to the mandrel, the mandrel surface advantageously has a surface finish in the range of about 10 to about microinches. Such a surface finish can be provided by the mill or can be obtained by means such as scratch brushing, light sand blasting, etc.

In carrying the invention into practice, it is preferred to deposit electronickel in a low-stress condition so that satisfactory adherence of the electrolytic nickel upon the exposed cathode areas will be achieved. Thus, it is advantageous that the tensile stress level in the deposit be not higher than about 6,000 pounds per square inch (p.s.i.) and between about 8,000 p.s.i. compressive and about 6,000 p.s.i. tensile as measured by the Brenner- Senderoff contractometer. When stress is controlled to this low level, cathode nickel segments as large as about 2 inches by 2 inches can be produced without encountering separation of the cathode nickel segments from the cathode sheet during the plating operation. It will be appreciated that the size of the conductive cathode areas, or islands, which may successfully be employed without encountering undesirable separation of the electrolytic nickel segments deposited thereon, varies in relation to the stress level which is maintained in the deposit. Thus, when lower tensile stress levels than 6,000 p.s.i. are maintained in the deposit, cathode nickel segments one-fourth inch to three-eighths inch in thickness and larger than 2 inches by 2 inches can be produced successfully, i.e., without encountering separation of the deposit from the mandrel during the plating operation. A tendency for lifting of nickel electrodeposits having a rectangular shape at corners of conductive islands has been observed. Accordingly, it is advantageous to employ conductive islands having a circular or elliptical shape.

In order to obtain the required low stress level in the deposit, a concentration of about 0.005 to about 0.02, e.g., about 0.009 to about 0.01 1, grams per liter (g.p.l.) of sulfur dioxide and about 0.01 to about 0.1 g.p.l. of a leveling agent, e.g., hydracrylonitrile, are maintained in the electrorefining electrolyte. A preferred electrolyte also contains about 40 to about 70 g.p.l. of nickel, about 20 to about 55 g.p.l. of chloride ion, about 65 to about 150 g.p.l. of sulfate ion, about to about 25 g.p.l. of boric acid, about 40 to about 60 g.p.l. of sodium ion, has a pH of about 3 to about 5, with the balance essentially water. This electrolyte is operated at a temperature of about 100 F. to about 160 F. at a cathode. current density of about 10 to about 35 amperes per square foot (a.s.f.).

After the cathode nickel has been grown to the desired thickness on the cathode, the plated cathodes are removed from the electroreflning cell and the crop of refined nickel is removed from the cathode sheet. It is found that, provided proper control of deposit stress level and mandrel surface finish are exercised, the nickel readily separates from the cathode sheet. Furthermore, the individual nickel segments are readily separable along the original resist lines present in the cathode sheet if, in fact, they are adherent one to another. In the case where the resist lines are about the same width as the thickness of the refined nickel deposit, it is found that a load of about 500 pounds applied normal to the surface of a nickel deposit stripped from the mandrel will sever a A inch thick deposit 12 inches long along a line grown across an original resist line one-fourth inch wide. When the resist lines applied to the mandrel are wider than the thickness of the final cathode product, there is little tendency for the individual nickel pieces to adhere to each other and such pieces may readily be recovered as such during the stripping operation.

The stripping operation itself may be conducted in a number of ways. Thus, flexible plated mandrels may be passed through rubber rolls to strip the deposit, or they may be flexed in any other convenient manner to strip the nickel deposit therefrom. Heavier, more rigid mandrels can be treated by vibration, hammering, etc., to remove the deposit therefrom. As an aid in the stripping operation, the mandrel may be treated before deposition of nickel thereon to reduce adherence of deposited nickel thereto. Thus, the mandrel may be dipped in a solution containing about 0.1 to about 1 g.p.l. of sodium dichromate for about 1 minute and then washed with water. This treatment is effective when used upon mandrels made of nickel, stainless steel and other nickel-chromium and nickel-chromiumiron alloys. This treatment also assists in promoting the useful life of the mandrel.

For the purpose of giving those skilled in the art a better understanding of the invention and/or a better appreciation of the advantages of the invention, the following illustrative examples are given:

EXAMPLE I A nickel electrorefining electrolyte having a pH of about 4 containing about 56 g.p.l. nickel, about 54 g.p.l. chloride ion, about g.p.l. sulfate ion, about 50 g.p.l. sodium ion, about 15 g.p.l. boric acid, and the balance essentially water was prepared. About 0.04 g.p.l. hydracrylonitrile and about 0.01 g.p.l. of sulfur dioxide were introduced into the bath. A flat stainless steel cathode mandrel having a smooth cold rolled surface, about one-eighth inch thick and having dimensions of about 29 by 40% inches, was marked off with interconnecting lines of electroplating tape to provide conductive islands about 1 inchsquare. The minimum width of the tape was about one-fourth inch. The mandrel was degreased, inserted in the bath and plated with nickel using an average current density of 20 a'.s.f. at a temperature of F. to provide a nickel deposit oneeighth inch thick on each side of the mandrel. The plated mandrel was then removed from the bath and the nickel deposit was readily stripped therefrom as individual pieces.

EXAMPLE [1 Thirty flat lightly etched stainless steel mandrels having the dimensions described in Example 1 were marked off on both sides with nonconducting tape bearing evenly spaced 1% inch diameter holes such that the spacing between edges of the adjacent circular conducting islands was at least about one-fourth inch. Nickel was deposited on the mandrels in a single plating tank using the bath described in Example 1 and with a current of about 7,000 amperes being supplied to the tank'for time sufficient to provide deposits three-sixteenths inch thick on each side of each mandrel. At this thickness, the areas of nonconducting tape were bridged over with nickel. The plated mandrels were removed from the bath and the deposits stripped therefrom by impact. The deposits were readily dividable along the locations corresponding to the original areas of nonconducting tape applied to the mandrel and had a roughly hexagonal outline.

The deposit produced according to Examples 1 and II had a stress level of about 1,000 p.s.i. tensile and was smooth and white.

The combination of the sulfur dioxide and hydracrylonitrile reagents to control stress level in the deposit is entirely compatible with the standard sulfatechloride electrorefining bath and the purification cycle employed therewith and the bath can be maintained over long peroids of time without difficulty.

The use of the combination of sulfur dioxide and hydracrylonitrile as described hereinbefore in the electrorefming bath in accordance with the invention will introduce controlled amounts of sulfur, e.g., about 0.015 to 0.05 percent sulfur, and more preferably about 0.02 percent to about 0.025 percent sulfur, into the deposit and will result in electrolytic nickel having high activity. This material is in a highly desirable physical form for use in titanium plating baskets. Furthermore, the material corrodes smoothly in conventional nickel electroplating baths without splitting since the product contains no physical interruptions such as the starting sheet contained within usual sheared electrolytic nickel. During plating, the material settles smoothly within the plating basket as the corrosion proceeds so that hangups, bridging and formation of voids in the nickel material within the basket are mitigated or are avoided altogether.

It will be appreciated that the method contemplated in accordance with the present invention provides a number of advantages over the conventional method of shearing a cathode into suitable size. Thus, cathode nickel plated to predetermined size is readily distinguished on the basis of its physical appearance from sheared nickel. Thus, the individual nickel pieces have greatly reduced amounts of sharp edges as compared to the sheared product and have a characteristic peripheral elevated ridge on the outer face of each piece, i.e., the face in contact with the bath, which apparently is created by the lines of resist present on the mandrel. In addition, the method also provides a ready means for applying an identifying mark to each individual piece. This may readily be done by embossing the conductive islands on the flexible mandrel with an identifying mark which is then reproduced in the deposit. As an economical advantage, the shearing costs such as are attendant to shearing large nickel cathodes to the desired size are eliminated. Furthermore, the step of providing a nickel starting sheet as a separate operation is eliminated since the cathode nickel is grown to its full size in a single operation in accordance with the contemplation of the present invention.

It will also be appreciated that the electrolytic nickel produced in accordance with the invention is of substantial thickness, e.g., at least about one-sixteenth inch up to about one-half inch or even thicker, whereas the nickel thickness employed in decorative nickel plating is of a much lower order, e.g., only about one to about two thousandths of an inch.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

lclaim:

l. Electrolytic nickel in subdivided substantially square, circular or elliptical form and substantially devoid of physical interruptions characterized by high activity, an internal stress between 8,000 p.s.i. compressive and 6,000 p.s.i. tensile, a sulfur content of about 0.015 percent to about 0.05 percent, smooth corrosion and freedom from splitting when corroded electrolytically substantial freedom from sharp edges, substantial thickness and by a peripheral elevated ridge about each piece. 

